The requirement to provide a seal between separate elements is well known in a wide range of technical fields. Typically this is carried out to prevent passage of a fluid from one region to another, for example due to a requirement to maintain a pressure differential or to prevent the fluid from causing damage outside its use area.
Where the seal is between two articles undergoing relative motion then the problem becomes more difficult, because if the seal element is to be effective, the seal element needs to engage both articles. The motion then causes wear on the seal element. Additionally, the seal element can impart a force resistive to the motion.
In the oil industry for example different types of relative motion can be contemplated: both relating to movement of an item of equipment within a generally cylindrical casing. In the case of a casing housing for a drill, then the seal between the drill and the casing needs to be able to withstand the rotatory motion of the drill. In the case of a piston, its longitudinal motion along the axis of the piston and the piston housing causes the difficulty.
In both of these situations, too soft a seal material can result in rapid wear of the seal element. Too hard a seal material can result in a weak seal as the seal material does not engage well with the various articles. Alternatively, if the seal engages too strongly with the articles then it can inflict wear on these articles and also inhibit their motion.
Within an oil industry drilling operation it is important that an effective seal be maintained for as long a period as possible, as replacement of the seal element can be both hazardous and expensive. Moreover, some seal elements are in difficult locations many metres underground and so the replacement may not be easy. Further, some seal elements are used in locations where space is at a premium and so the horizontal area taken up by the seal element and the housing therefor should occupy as little space as possible.
In the particular examples given above, conventional seal elements are sacrificial and comprise a polymeric rubber material, often having a layer of lubricating oils between the seal material and the drill or piston. The material is often housed within a seal block affording access to replace the seal element when required. As indicated however this requires the operation being undertaken to be closed down and for the section containing the seal block to be isolated to prevent backflow from the drill hole.
It is an object of the present invention therefore to provide a seal to address the above problems. It is a further object of the present invention to provide an improved method of obtaining a seal which addresses the above problems and reduces the frequency with which downtime occurs.